3 phase to single phase back to 3 phase?

[Badasssapper67]

Hi all. I bought an old radial arm saw from a consignment shop. I was told it was 3 phase but the owners buddy "converted" it to single phase.
Plugged it in and it ran fine. Got it home dims the lights when starting it but other than that it ran fine. Tried to cut a 2x4 and it bogged out.
Im no electrical engineer but Im guessing his buddy cut two of the three phases out to get it to run, what do you guys think and how do I get this thing back to 3 phase 220v instead of single phase 120v?

I will upload pic's and model # info soon if that helps.

 

[Bobf]

My guess is it was "faked" to start up with capacitors someplace in the circuit and run on sgl phase 240V. A 3ph 208V motor will run on 240 but the effective power is reduced by a rms factor of .707 ie. a one hp motor will be a .707hp motor.

 

[lametec]

Either that or it's a single phase 240V motor instead of 120V. Check under the motor cover to see what it's wired as, and if it can be changed.

 

[rockwithjason]

My guess is it was "faked" to start up with capacitors someplace in the circuit and run on sgl phase 240V. A 3ph 208V motor will run on 240 but the effective power is reduced by a rms factor of .707 ie. a one hp motor will be a .707hp motor.

this is very likely. you may need to convert to a single phase motor, a vfd or a rotary converter.

 

[larry_g]

When you got it home, What voltage did you plug it into? 120 or 240? Is there some 'box' of electrical components that make the conversion? I'd guess that it is using a static converter arrangement ans should be run on 240v. Doing so will give you 2/3 hp of the rated hp.



lg
no neat sig line

 

[Badasssapper67]

The owner I bought it from insisted that it was "converted" to run on 120v. As I was loading it on the trailer he reminded me one more time, "remember it will only run on 120v". At the time I thought that was a little strange.
There isnt anyplace to easily hide capacitors and I would swear he said something about snipping wires but I have a terrible memory...
Right now Im trying to upload pic's onto photo bucket......

 

[bisley45]

Can you post a picture of the saw and the motor info badge ?

 

[Badasssapper67]

[/URL][/IMG]

 

[Badasssapper67]

[/URL][/IMG]

 

[Badasssapper67]

The plug I have that goes into the wall is for 120v, but the cord that goes from the motor to the arm is 220 or whatever household power is.
Clearly Im no electrician, I never got to understand if there is a difference between 220, 230, 240...

 

[Bobf]

The plate on the motor indicates it is capable of dual voltage sgl phase opr'n.
There might be a diagram behind the plate on the motor to reveal connections for each voltage?? The confusion about 220/230/240 is just that. Most homes have three wire service with two legs commonly referred to as opposite phase. Most boxes are set up to balance breakers between the phases. The different voltages referred to goes back to different areas of the country using different amounts supplied to houses when electrical lighting first became available. ie. some area used 110, others 120, and 130, thus multiplying X2 we ended up with 220, 230, & 240. This is over simplification but basically accurrate.

 

[jwvess00]

Hi there!

That's not 3 phase. 220V is still single phase, just 220V.

That motor can be wired to run on 120V or 220V. Either will work.

 

[jwvess00]

Hi there!

I've heard more than one person call 220V 3-phase. It's not. It is still single-phase power. 3-phase is generally used inthe U.S. by commercial and industrial places, but not residences.

3-phase shows up in a variety of voltage levels for equipment, but the most common I've seen is 440V (or 480V, same thing -- just like 110V/120V is the same service). 277V is a not-uncommon power for commercial lighting, by taking a single phase from a 3-phase feed. If you're buying used fluorescent lighting from a commercial or industrial setting, check the ballast to see if it will run on 110V.

My vote for the weirdest (common) power is in parts of Japan -- 100V, 50 Hz. At work we have to design power supplies to work on that power, and running at that input power lowers the power supply's efficiency.

It hasn't been that long since ConEd stopped regular DC (!) service:
http://www.coned.com/newsroom/news/pr20071115.asp

 

[Stuart in MN]

Per the motor tag it takes 20 amps at 120vac, so if you plugged it into a regular wall outlet that's probably why the lights dimmed - your wall outlets are on either a 15 or 20 amp circuit, and even a 20 amp circuit is marginal for proper operation. I'd reconnect the motor so you can run it on a 240vac 20 amp single phase circuit instead. There should be wiring connections marked somewhere on the motor, possibly inside the cover.

 

[Badasssapper67]

Thanks guys!

 

[airdale]

If you have an electric clothes dryer, that is an example of a 240v 1 phase service. If you want to change the motor to utilize 240v you will also need an 240v outlet, fed from a properly sized breaker. And a matching power cord and plug. Do not attempt this yourself. Get qualified help or hire an electrician.

Then your motor will run cooler, last longer, and have better performance.

 

[C96]

Although the motor nameplate indicates 115/230 volts and 20/10 amps it would be best to re-tap the motor for 230 volt operation.

Just as Stuart in MN said, you are basically overloading the circuit plugging that saw into a standard household receptacle. The saw for 115 volt operation should have been equipped with a NEMA 5-30 plug preventing you from plugging into that standard outlet. That’s why the lights dimmed and the saw was gutless. If your going to run that saw on a 115 volt circuit you would need a minimum of a 25amp circuit. Typically this would be a circuit run with 10 AWG wire and a 30 amp single pole breaker. This type of circuit is basically non existent in a residential setting, but can be found in some commercial installations where a specific piece of equipment requires a 30 amp circuit at 120 volts. You will also see such a circuit at RV parks, but with a different plug configuration TT-30.

Again, best would be re-tapping motor for 230 volt operation and wire accordingly.